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i v <br /> 0 <br /> 16 A S S O C I A T E S I N C <br /> Soil in boring MW1 consisted primarily of fine soils consisting alternated layers of silt (ML to <br /> MH) and clay (CL) to a depth of 24.5 feet bgs, the maximum depth explored. <br />' 3.2 ilydrogeologyy <br />' Water level measurements were collected from well MW1 on February 26, 1999. The water <br /> level was measured at 9.95 feet from the top of the well casing. A summary of groundwater <br /> monitoring data is presented in Table 2. <br /> The site's underlying groundwater gradient could not be determined with a single measurement <br /> point, however regional groundwater flow is estimated to be eastward based on San Joaquin <br />' County Flood Control and Water Conservation District data (Lines of Equal Elevation of <br /> Groundwater, Fall 1997). <br />' 4.0 ANALYTICAL RESULTS <br /> 441 Soil Analytical Results <br /> Soil samples collected from boring MW1 contained concentrations of TPHg (2.2 to 1,900 part <br /> per million (ppm)), toluene (7.3 ppm), ethylbenzene (0.0074 to 18 ppm), and total xylenes (0.045 <br /> to 120 ppm). <br /> Benzene and fuel oxygenates were not detected above laboratory method detection limits. <br /> Analytical results of soil samples are summarized in Table 1. <br /> 4.2 Groundwater Analytical Results <br />' The groundwater sample collected from well MW 1 contained concentrations of TPHg (3,900 <br /> part per billion (ppb)), toluene (86 ppb), ethylbenzne (100 ppb), total xylenes (530 ppb), and <br />' MTBE (12.5 ppb). <br /> Neither benzene nor the remaining oxygenates fuel additives tested for, were detected above their <br />' respective laboratory method detection limits. It should be noted however the laboratory method <br /> detection limits were raised due to the elevated levels of gasoline observed in the sample. <br /> A review of the analytical data indicates that the MTBE concentration in groundwater exceeds <br /> the current California water quality goals for drinking water. The California Department of <br /> Health Services (DHS) adopted a secondary drinking water standard (maximum contaminant <br />' level, MCL) of 5ppb for MTBE, effective January 7, 1999. The primary MCL established DHS <br /> for MTBE is currently under development, however Cal/EPA's Office of Environmental Health <br /> Hazard Assessment (OHHA) has adopted a 13 ppb Public Health Goal for MTBE which is being <br /> w:l]72921reportslsumwc1.doc 4 <br />